1. Field of the Invention
The present invention relates to gearset transmissions, and particularly large gearset transmissions with a wide variety of speeds suitable for use in work vehicles such as agricultural and industrial equipment.
2. Description of the Related Art
There are a great many powershift transmissions known having a large variety of speeds. Such variety of speeds is particularly useful for large vehicles, and especially work vehicles such as agricultural and industrial tractors. Such vehicles may need a dozen or more speeds in a very small range, e.g., 0.5 to 5 kilometers per hour, and just a few at higher speeds, e.g., up to 40 kilometers per hour.
Such vehicles typically have a large mass, or are under a significant load (for example, plowing), so that the change in energy levels between the rotating components of the transmission should be held to a minimum between any two successive speeds. This is necessary to minimize the time required for a shift, thereby allowing a smoother shift and preventing the vehicle from coming to a lurching halt. At the same time, the transmission size must also be held to a minimum in order to fit into an existing vehicle.
Funk Manufacturing currently produces a powershift transmission for Ford/New Holland row crop tractors which provides 18 forward speeds and 9 reverse speeds. To do this, nine clutches and attendant gears are arranged with six clutches in a speed section and three clutches in a range section. The six clutches in the speed section can provide nine useable gear ratios, while the three clutches in the range section provide two forward ranges and one reverse range.
While at first it might appear that nine additional speeds could be provided simply by adding another forward range, this is not practical in reality. First, there is the simple limitation of space. Second, and more important, the necessary readjustments to the gear ratios of the speed gears required so that the bulk of these ranges will still be in the desired, limited range of, e.g., 0.5 to 5 kilometers per hour, would produce a very undesirable range of reverse speeds. In addition, the momentum which must be changed upon shifting from one of these ranges to another would be undesirably high.